1. Field of the Invention
The present invention relates to an infrared light reflector. Precisely, the invention relates to an infrared light reflector having an infrared light reflective layer containing a cholesteric liquid crystal compound, which is used mainly for heat shields for windowpanes in buildings, vehicles, etc.
2. Description of the Related Art
Recently, with the increase in the interest in environment and energy, the needs for energy-saving industrial products are high, and as one of them, glass and films are desired that are effective for heat shields for windowpanes in houses, cars and the like, or that is, for reducing thermal load from sunlight through windowpanes. For reducing the thermal load from sunlight, it is necessary to prevent transmission of the sun's rays in any of the visible range or IR range of the sunlight spectrum.
A method of using a cholesteric liquid crystal phase in an infrared light reflector has been proposed. For example, as disclosed in Patent Reference 1, by forming one cholesteric liquid crystal layer on both sides of a λ/2 plate, a light circularly-polarized in one direction can be selectively and efficiently reflected within a range of from 700 to 1200 nm of the sunlight spectrum.
For producing an infrared light reflector capable of selectively reflecting the light in a broad range of the sunlight spectrum, generally employed is a laminated cholesteric liquid crystal layer formed by laminating a number of cholesteric liquid crystal layers in a mode of coating (see Patent Reference 2).
Patent Reference 2 discloses a coating composition for forming a liquid crystal layer, which contains a cholesteric liquid crystal material and a solvent and in which the solvent has a specific composition. In this, the coating composition is applied onto a substrate to form thereon a smooth liquid crystal layer with no trouble of coating unevenness. In addition, the patent reference further discloses addition of any other polymerizable compound than polymerizable liquid crystal material for the purpose of enhancing the physical properties or the chemical properties of the liquid crystal layer, concretely exemplifying a bisphenol A-type epoxy resin, etc.
On the other hand, Patent Reference 3 discloses a liquid crystal composition for cholesteric liquid crystal containing a specific rod-shaped liquid crystal compound, though nothing is referred to therein relating to the number of the layers to be laminated. In this, liquid crystalline polymerizable compounds, polyfunctional polymerizable compounds and others are shown as examples of the polymerizable compound that differs from the specific rod-shaped liquid crystal compound. In Examples in the patent reference, disclosed is increase in the surface hardness through addition of the polymerizable compound that differs from the specific rod-shaped liquid crystal compound.
On the other hand, recently, for controlling the alignment of a liquid crystal compound, addition of a fluorine-containing alignment controlling agent has become investigated (Patent Reference 4). However, there have been known few cases of adding a fluorine-containing alignment controlling agent to a coating composition for an infrared light reflector having an infrared light reflective layer containing a cholesteric liquid crystal compound.    Patent Reference 1: Japanese Patent 4109914    Patent Reference 2: Japanese Patent 4216568    Patent Reference 3: Japanese Patent 3900987    Patent Reference 4: JP-A 2005-99248